1,406. How Can One Read From a Scroll While He's Writing It?

Hilchos Megillah v’Chanukah 2:6

The idea that one can fulfill his obligation by reading the megillah while writing one only applies when one intends to fulfill his obligation by reading from the scroll that he is copying. If one intends to fulfill his obligation by reading the scroll that he is currently writing, he does not fulfill his obligation. This is because one can only fulfill his obligation by reading from a scroll that was already completed at the time he read it.

Hilchos Megillah v’Chanukah 2:7

If someone makes a mistake while reading the megillah and reads it in an imprecise fashion, he fulfills his obligation. This is because we are not obligated to read the megillah with such precision. One may fulfill his obligation to read the megillah either standing or sitting; this is true even when one is reading it for the congregation. However, out of respect for the congregation, it would be appropriate for a person not to read the megillah for a congregation while seated. If two – or even ten – people were to read the megillah in unison, both those reading and those listening fulfill their obligation. An adult and a child may read the megillah in unison, even for a community.